Nagios is a powerful, enterprise-class host, service, application, and network monitoring program. Designed to be fast, flexible, and rock-solid stable. Nagios runs on *NIX hosts and can monitor Windows, Linux/Unix/BSD, Netware, and network devices.

JasperReports Library, the world's most popular open source business intelligence and reporting engine and JasperReports Server, the most popular open source interactive report server built-on JasperReports Library

JasperReports Server is a powerful, yet flexible and lightweight reporting server. Generate, organize, secure, and deliver interactive reports and dashboards to users with a web based BI Platform. Available as an open source community edition download as well as a commercially licensed, enterprise-grade business intelligence solution.

iText is a PDF library that allows you to CREATE, ADAPT, INSPECT and MAINTAIN documents in the Portable Document Format (PDF):
- Generate documents and reports based on data from an XML file or a database
- Create maps and books, exploiting numerous interactive features available in PDF
- Add bookmarks, page numbers, watermarks, and other features to existing PDF documents
- Split or concatenate pages from existing PDF files
- Fill out interactive forms
- Serve dynamically generated or manipulated PDF documents to a web browser
iText is used by Java, .NET, Android and GAE developers to enhance their applications with PDF functionality.
Several iText engineers are actively supporting the project on StackOverflow: http://stackoverflow.com/questions/tagged/itext

Mondrian is an OLAP (online analytical processing) engine written in Java. It reads from JDBC data sources, aggregates data in a memory cache, and implements the MDX language and the olap4j and XML/A APIs.

ADempiere Business Suite ERP/CRM/MFG/SCM/POS done the Bazaar way in an open and unabated fashion. Focus is on the Community that includes Subject Matter Specialists, Implementors and End-Users. We forked and survived Compiere which is now closed.

Zenoss Core is today's premier, open-source IT monitoring solution. Using a single, web-based console and agentless technology, you can monitor and manage the performance and availability of all devices in your IT infrastructure (network, server, storage, applications, converged infrastructure, virtualization/cloud).
The power of Zenoss Core begins with its in-depth IT inventory and configuration database. Zenoss creates this database by discovering managed resources -- networks, servers, storage, and other devices -- in your IT environment.
Once Zenoss Core discovers the IT infrastructure, it automatically begins monitoring the performance of each device and provides event and fault management capabilities. These capabilities help drive IT operational efficiency and productivity by automating many of the monitoring, notification, alert, escalation, and remediation tasks you perform each day.